This invention relates to new substantive dyes, to preparations for coloring and tinting keratin fibers, more especially human hair, containing these dyes and to the use of these preparations.
Preparations for tinting and coloring hair are an important type of cosmetic product. They may be used to give the natural color of the hair a light or relatively dark shade, to obtain a totally different hair color or to cover unwanted color tones, for example gray tones, according to the wishes of the particular user. Conventional hair colorants are formulated either on the basis of oxidation dyes or on the basis of substantive dyes according to the required color or the permanence thereof. In many cases, combinations of oxidation dyes and substantive dyes are also used to obtain special shades.
Good dyes are distinguished by high coloring strength. They are also required to show high fastness to perspiration, washing and light. In addition, they are expected to be toxicologically and dermatologically safe. It is also of advantage if the substances are highly soluble in various basic formulations.
Colorants based on oxidation dyes lead to bright and permanent color tones. However, they do involve the use of powerful oxidizing agents such as, for example, hydrogen peroxide solutions. This can damage the hair to be colored. Such damage then has to be repaired with suitable hair-care products. In addition, contact of the skin with these colorants can produce unwanted reactions in very sensitive people.
Colorants based on substantive dyes do not require oxidizing agents and can be better formulated at pH values around the neutral point. However, a major disadvantage of colorants based on substantive dyes is the poor fastness to washing of the colored hair. Consequently, the ability of the dye molecules to attach themselves to the hair and the luster of the colored hair are not entirely satisfactory in many cases.
To develop fashionable colors, red color tones have to be obtained. This is frequently achieved by the use of 2-nitro-p-phenylenediamine derivatives. However, these derivatives are often inadequately soluble or dispersible in water. If the dye cannot be solubilized in the coloring medium, uneven colors are the result. There is also a high risk of only weak colors being obtained.
To improve level dyeing and to broaden the range of shades, substantive dyes are also commonly used in oxidation hair colors. Unfortunately, the substantive dyes normally used show poor stability to reducing and oxidizing agents.
Accordingly, there is still a demand for substantive dyes which do not have any of the disadvantages mentioned above.
It has now surprisingly been found that certain 2-nitro-p-phenylenediamine derivatives satisfy the requirements substantive dyes are expected to meet to a high degree.
In a first embodiment, therefore, the present invention relates to preparations for coloring keratin fibers, more particularly human hair, which contain at least one 2-nitro-p-phenylenediamine derivative corresponding to formula (I): 
in which R1 to R4 independently of one another represent hydrogen, a C1-4 hydroxyalkyl group or a saturated, mono- or polyunsaturated C7-8 ring which may optionally be substituted by a C1-4 alkyl group, a halogen atom, a hydroxy group or an amino group and X is hydrogen or a halogen atom, with the proviso that at least one of the substituents R1 to R4 is a C7-8 ring, in a carrier suitable for coloring.